Ralph St. John is well into his 70s, but his stocky arms show that he is a man accustomed to hard labor. In Willets Point in the New York borough of Queens, he founded a general contracting company 36 years ago. He hoped to leave it to his son.

Now, however, Mr. St. John's business is one of 250 in an industrial zone that New York City has slated for redevelopment using eminent domain.

With the Senate's expected confirmation of Sonia Sotomayor to the Supreme Court, many small-business owners are fearful that the future court will make it that much easier for powerful developers to evict them for any reason.

Why would Judge Sotomayor make a difference? At issue is a precedent that property-rights experts say Sotomayor helped set in 2006 in a case between a private developer empowered by eminent domain and a small-business owner like St. John.

Currently, there are nine eminent-domain cases with potential constitutional implications being litigated in state courts, according to the Institute for Justice, a law firm based in Arlington, Va., whose focus includes private-property rights. Somin, who testified at last week's confirmation hearings, and other legal experts worry that should any of these nine cases come before the Supreme Court within the next five to 10 years, small-property owners will lose their last vestige of protection.

In 2005, the high court took on the eminent-domain case of Kelo v. New London. In a controversial decision, the justices said that local governments could use eminent domain to spur economic development that would benefit the public.

But Kelo also reaffirmed that no property can be condemned and transferred to a private party under pretext of public benefit.

Bart Didden thought that his suit against the Village of Port Chester, N.Y., was such a pretextual case. But in 2006, a three-judge panel of the Second Circuit Court of Appeals, which included Sotomayor, upheld the village's actions in a one-page opinion.

CVS approached Mr. Didden to build a pharmacy on land that had been designated a redevelopment area. The village's eminent-domain proxy, a private developer, demanded either $800,000 compensation or a 50 percent stake in the project, Didden says. Didden refused, and the Village of Port Chester filed the following day to condemn his property.

The developer maintained in court filings that the proposed settlement was fair compensation for a standard business dispute.

Somin sees it differently. "If [Didden] was not an unconstitutional pretextual condemnation," he says, "it is hard to see what would be."

At her confirmation hearings, Sotomayor stood by her handling of the case.

Didden, she said, had filed suit three years after New York's statute of limitations had run out for challenging eminent-domain proceedings. Also, Sotomayor said, the points in the Kelo decision did not apply because the private developer was within his rights, given by the state, to demand a settlement.

"I'm going to lose X amount of money," she said, reenacting the developer's argument for the Senate committee. "So you pay me that for me not to do what I'm entitled to do under the law.' "

Didden counters, "I don't think [the Senate Judiciary Committee members] really understand the gravity of what my case was about and what it did."